40 RANGE INVESTIGATIONS IN ARIZONA. 



McCleary's did not reach the area in question, and as nearly as can V)c 

 judged the rainfall here at this period was little if any greater than at 

 Tucson. The etitect upon the deep sands of the washes, however, was 

 considerable, no doubt, and the deep roots of the shrubs were able to 

 profit b}" it. 



The winter season is characterized by an abundant (relative) growth 

 of short-lived annuals. Some of these, as before stated, start their 

 growth in October, or even September, at the close of the summer 

 rainy season. Among these may be mentioned Pectocarya linearis^ 

 altilerilla, Indian wdieat, and a large number of boraginaceous plants 

 which furnish a great deal of feed. Between this time and the 1st of 

 February (it is not definitely known at what time, and, indeed, the 

 time varies owing to the variation in precipitation) there appear a host 

 of other short-lived plants, a large number of which are of some for- 

 age value. These are ephemeral, especially in their effect upon the 

 landscape and in their forage utility, although they are really in the 

 vegetative state a considerable period. The time of maturity of these 

 winter and spring annuals in the same season is very variable, there 

 Ijeing- from two to three weeks' difference between the mesas about 

 Tucson and the northern slope of the Santa Rita Mountains or the east- 

 ern slope of the Babuquivaris. This vernal development is mostly con- 

 fined to altitudes below 4,000 feet in southern Arizona, the regions 

 above this having really but one prominent vegetative season. The 

 cause of this is mainly the lower temperatures of the higher altitudes, 

 there being too low a temperature for the growth of the annuals at a 

 time when the winter and early spring moisture is present. By the 

 time the temperature is high enough for plant growth the moist con- 

 ditions have disappeared, and there is practically no growth of vege- 

 tation, except during the summer rainy season. A very large part of 

 the best pasture lands of this section, therefore, has but one season of 

 plant growth. 



The summer season is characterized by the production of grasses of a 

 great variety of species. Upon the lowlands the greatest development 

 is upon the flooded areas, which were much more abundant formerly than 

 they are now, owing to the excessive erosion which has taken place dur- 

 ing recent years. Upon the mesas there is but littledevelopmentof per- 

 ennial grassesas a usual thing, unless these mesas be high. In favorable 

 places and in favorable seasons there are a few perennials which make 

 considerable feed. Upon the mesa swales galleta {Ililaria mutica) is an 

 important grass, while upon the less favorable situations species of 

 p-rama srrass sometimes make a thin growth. It is on the foothills and 

 mountains that the grasses make their best and most pronounced 

 growth. Here the rainfall Is more abundant during the summer season 

 than upon the lower areas, although there may not be such a difference 

 in the winter rainy season, and the growth of grasses is proportionately 



